Industrial heat treating furnace



Oct 6, 1942- c. E. PEcK 2,297,798

I INDUSTRIAL HEAT TREATING FURNACE .Filed Maron ie, 1940 2 sheets-sheet1,

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ATroRNEY omu e, 1942. C. E. PECK 2,297,798

INDUSTRIAL HEAT TREATING FURNACE Filed March 1e, 1940 2 Sheets-sheet 2wlTNEssEs; S r

Paieoied Oei. 6, 1942 i INDUSTRIAL HEAT rnEaTiNGrFUaNAcE Clarence E.Peck; Wilkinsburg, Pa., 'asslgnor to Westinghouse ElectricaManufacturing Company, East Pittsburgh, l?a a corporation ofPennsylvania l Application Maren 1s, 1940, serai No. 324,409v

' s claims. `(ci. zes- 5) 'I'his invention relates to charge-supportinghearths for heat-treating furnaces, preferably of the bell and hoodtypewhich are to be operated at' fairly high temperatures. and in whichthe charges are to be heat-treated while enveloped by a protective orcontrolled gaseous atmosphere.

It is an object of my invention to provide'a relatively long hearthcapable of withstanding high temperatures in the neighborhood of 1600 tol800 F., and above," which will have provisions for permitting all thenecessary differential expansions between its hot parts inside thefurnace, and the cooler'outer parts without damage. In this respect itis a further purpose of my invention to so construct and divide themetallic parts `of the hearth so that their displacements, due toexpansion and contraction,

wi1l.be reduced, keeping the maximum displacement of any part torelatively small proportions: Additionally, in accordance with thisaspect .of my invention, the spaces between the divided parts areprovided with suitable sealing or closure i means.

It is a further object of my invention to provide a hearth comprising anon-metallic refractory base portion which will not chemically react,especially in a hydrogen atmosphere, with a metallic charge-supportingmeans which it supports.

It has beenfound by experience that if the metallic charge supportingmeans was made of an inexpensive ferrous metal, such as mild steel, themetal would react chemically with the nonmetallic refractory directlysupporting it, particularly during the purging of air and moisture fromthe furnace by a continuous flow of a controlled hydrogen atmosphere;the melting point and strength of the refractory being adverselyaffected. It is my opinion that as the temperature of the furnaceincreased, any small layer of iron oxide on the surface of the metal wasreduced by the hydrogen, and if such reaction occurred where the metalwas in contact with the refractory. the refractory material would fuseand melt, forming a material of a much lower melting point than theoriginal refractory.

Accordingly; it is an object of my invention to provide a hearth of thetype described which utilizes relatively inexpensive materials for thecharge plate and the non-metallic supporting refractory, but which willinclude means for limiting the deterioration of the non-metallicsupporting refractory. v

It is 'a further object of my invention to provide means to convey thevcontrolled atmosphere through the hearth to the inside of the furnace,preferably inside the hood enclosing the hearth. To this end I providesuitable gas-sealing means which will enable all of the required inletand discharge pipes to expand independently of each other, and thus Iovercome a difficult expansion between parts having considerablydifferent temperatures. All welded joints and metallic type expansionjoints which may crack and fail are eliminated in my construction.

In accordance with my invention, the hearth comprises a non-metallicrefractory base upon which rests a base plate made of a plurality ofsections having spaced edges so that the sections may expand andcontract toward and away from each other. However, a suitable means isprovided covering and sealing the spaces between these edges, thisvmeans being substantially gastight, but not interfering with thedisplacement of the sections. Additionally, theouter -periphery of thebase plate preferably is provided with depending lips or flanges whichextend into a suitable gas-sealing channel around the base portion ofthe refractory base, the flanges and channel being also provided withmeans, substantially gas-tight, which will permit these parts to expandand contract without extensive displacement. vention, the anges areprovided with guiding means for positioning the lowerv edges of thefurnace hood suitably in the same gas-sealing channel into which theflanges extend.

In the preferred form of my invention, the base plate takes the formofga container for holding a nnely divided refractory sand, such asalumina vor magnesia, which provides a sand bed that can be easilylevelled. A charge-supporting plate, smaller than the container, restson this bed, with its edges inward of the'inner periphery of thecontainer to allow for maximum changes in the dimensions ofthe platewith variations in temperature. A hearth, embodying a refractory sandbed confined .in a container, with a charge plate resting on the bed, isdescribed and .claimed in Patent No. 2,189,624 of J. H. Bramble, issuedFebruary 6, 1940, and assigned to the Westinghouse Electric 8LManufacturing Company. 1

Many other objects and features of my invention, and details thereof, inaddition. to those aforesaid, will lbe apparent from the followingdescription thereof which is to be taken in con- Junction with thedrawings, in which:

Figure 1 is a verticali. longitudinal, sectional, 7

view of a hearth employing my invention, and

As a further novel feature of my inhood omitted for clarity ofillustration;

schematically showing a. hood for enclosing a charge to be placed. onthe hearth;

Fig. 2 is a plan view of the hearth, with the Fig. 3 is an enlargedfragmentary, vertical, sectional view, on the line III-III of Fig. 2,more fully showing the constructional details by which the controlledatmosphere is directed into the charge heat-treating space under thehood, `a preheating conduit system being within the hearth;

Fig. 4 is an enlarged side view of a detail;

Fig. 5 is a fragmentary, vertical, sectional view, somewhat enlarged, ofa modified form of hearth construction, and

Fig. 6 is a schematic, vertical, sectional view, on a much reducedscale, of a furnace incorporating my invention. v i

My invention is primarily applicable to a belltype furnace such as shownvery schematically in Fig. 6, although my invention is not necessarilylimited to this type of furnace.

The bell-type furnace comprises a support or base 2 of a non-metallicrefractory material provided with an upwardly protruding base wallportion 4 forming part of a hearth which also includes' a container,indicated in its entirety by the reference numeral 6, supported on thebase portion,v and comprising a multi-section base plate 8 andmulti-section sides I0. The container is,iilled with a non-metallicrefractory sand' I2 which can be levelled, and wl :h supports a fiatcharge plate I4 on its surface, the charge plate being a single piece ofsuitable metal having a periphery Within the inside periphery of thesides l0 and being suitably spaced therefrom at all points so that theplate may expand and contract without contacting the sides. A hearth ofthis general character is shown in the aforementioned patent.

A removable heating bell I6 having side wall heating elements I8 can beremovably set on the base 2 which has an outside sealing channel 20around it. This channel is lled with any suitable sealing substance forreceiving a depending lip 22 of an outer metallic shell or casing 24,provided for the bell. A similar outer metallic casing 26 is providedfor the outside of the base 2, so that the bell and base are rendered,as far as possible, gas-tight, as is customary in the art. The baseportion 4 has a sealing means 30 around it for receiving the lower edgesof a removable metallic hood or shield 32 so that any charge placed uponthe hearth willbe suitably enclosed within a heat-treatment space 34defined by the hood and hearth. l

In the preferred form of bell-type furnace to which my invention isapplied, the heating units I8 extend below the charge plate I4 so thatall parts of any charge within the heat-treatment chamber 34 will beadequately heated.

The sealing means 20 and 38 may include any suitable sealing medium,such as finely divided non-metallic refractory sand for the innersealing means 30, and a similar sand or a suitable liquid for the outersealing means 20.

The base portion 4 has a suitable gas inlet means schematicallyindicated in Fig. 6 at 36, and in greater detail in Figs. 1, 3 and 5,for a protective gas to be discharged after being preheated,

n along the inside surfaces of the hood.

Referring more particularly to the embodiment l of my invention shown inFig. 1, the base portion 4 is shown as comprising a continuousrefractory wall which may be made of any suitable highportion 4 is thecontainer 6 with its base plate 8 comprising a plurality of separatesections, shown in this instance as two sections 40 and 42, the facingvertical edges44 and 46 of which are spaced from each other to providean intervening space 48. A platel 50 has one edge welded, or otherwisesecured, to the section 40 and its other edge slidable on top of theother section 42. This plate 50 covers the space 48 so that thecontainer can be filled with sand to provide the sand bed I2. Secured toand coextensive with the other vertical edges of the sections 48 and 42are upstanding lips or flanges 52 and 54, respectively, comprising upperportions forming the sides I0 of the container 6, and lower portionsextending into the sealing means 38. y

In order to render these vertical flanges substantially continuous alongthe space 48, suitable closing members 56 and 58 are provided on eachside of the hearth, each having an end portion welded or otherwisesecured to the part of the flange 52 in proximity to the space 48, withthe other end portion slidably contacting the flange 54. The members 56and 58 have outer sides which are of substantially the same height andabut the outer surfaces of the flanges 52 and 54, and have inner sideswhich abut the inner surfaces of theanges 52 and 54. The inner sides ofthe members 56 and 58 are of a height substantially equal to thedistance from the top surface of the plate 50 to the top of the ilanges52 and 54. The two si'des of each of the members 56 and 58 are bridgedby a cross piece so that each member is, in eifect, of inverted U-shapewith an inner leg shorter than the outer leg which .extends into thesealing means 30.

The sealing means 36 comprises a generally U-shaped channel 6I) forconmng the refractory sealing sand 62 into which the flanges 52 and 54,including the outer sides of the members 56 and 58, extend, and in orderto provide suitable expansion means for the channel 60 it is also splitinto a pair of spaced sections which are edgewise separated in theregion when the container 6 is split. Insert troughs 64 and 66 bridgethe space formed by the separated edges of the channel 60, these troughsclosely tting the interior surfaces of the channel 60, so as to renderthe latter, in effect,l continuous. One end portion of each of thesetroughs may, if desired, be secured to one section of the channel 1 60,the other end portion of each trough being in slidable contactingrelation with the corresponding side of the other section of thechannel.

Each section of the container 6 has a freedom of movement for expansionand contraction in space 48 and the end portions of the sand seals 30,the small closure means comprising the plate 50 and the invertedU-shaped members 56 and 58 keeping the variable space 48 covered duringsuch displacement. Additionally, the sections of the channel 60 can alsoexpand and contract, the closure troughs 64 and 66 keeping the channelcomplete at all times. Consequently, the container 6 is full-floatingwith provisions for expanding and contracting at a plurality of pointsdistributed along its length so that each displacement is relativelysmall as compared to what would have been the displacement if thecontainer had been made solid. In other words, the movement of any partof the cons therewith to form a sand tainer due to great variations intemperature is kept small in my novel construction. v

In order to convey. preheated protective at -mosphere into theheat-treatment chamber I4,

I prefer to provide the base portion 4 and the base oi' thecontainervwith suitable apertures v in which may be disposed 4the gasinlet system Il which has means for allowing all of the necessarydifferential expansions and contractions between the hotinner parts ofthe furnace .and cooler outer parts of the pipe system. To this end theouter casing 24 oi the base is provided withan aperture toasrbyiwelding, gas 'inlet pipes 10. In this particular embodiment. twosimilar inlet systems are provided, one at each end of the container.

Each inlet pipe 'I0 extends through a sand sealing means comprisingl acylindrical outer member 12 about the pipe 10 and cooperating sealingmeansfor conilning the sealing sand 14.- Each` of the sections 40 and 42is also provided with apertures defined by stepped surfaces 'l0 forreceiving a cover plateplll which has a plurality of holes into whichare fitted L-shaped pipes 00 which are embedded in the sand bed |2. Aconduit 02 is directly `below the cover plate 10, having one edge in thesealing sand 14 and projecting upwardly in proximity to the cover plate18. Gastightly secured to the upper outside edge of the conduit 82 is anannular plate 04, and depending downwardly therefrom and alsogas-tightly secured thereto is a cylindrical sealing member 00 extendingdownwardly into aI sealing sand bed l0 confined in an annular sealingchannel 90 about the pipe 02, the sealing channel 00 being gas-tightlysecured to a` section of the base 8 about the aperture for the coverplate 10. A

g handle bar` 02 is secured acrossthe top of the pipe section 82 so thatit may be readily removed, or inserted in position.

The L-shaped pipes 80 have thei longerv legs substantially horizontal,the legs passing through suitable holes 4in the flanges 52 and 54, andterminating somewhat above and slightly outward from they inner side ofthe channel 00, where the protective atmosphere is discharged. A guard96, closed at the bottom and sides, and open at the top, protects theoutlets of the horizontal legs of the discharge pipes 80 and alsodiverts discharging gases upward. The vertical legs of the pipes 00provide duct means for conveying the gases to the horizontal legs of thepipes from` the distributing chamber below the cover plate 18 and formedtherewith in conjunction with the channel 90, the sealing member 00, andthe annular plate 04.

The sand bed I2 covers the pipes 80 and may be levelled to support theflat charge plate I4 in accordance with the teachings of the aforesaidBramble patent.

- In order to prevent damage to the guard elements 96 during lowering ofthe hood, and also toguide the hood into vide guides |00 spaced alongthe anges 52 and 54, and secured thereto, the guides having inclinedupper 'surfaces for directing the hood evenly into the sealing channel30.

I have found that in furnaces for heat-treating a charge in the presenceof a large amount of a reducing gas such as hydrogen, a ferrous metalplate directly in contact with the supproper position, I pro- Aportingrefractory tile caused chemical reaction between the refractory tile andthe plate if the plate were made of a relatively inexpensive which issealed,

ferrous metal such as mild steel. In order to prevent this reaction andto reduce the use of a'la'rge amount of expensive non-reacting heat- 4resistant metal, I have found that by interpos- 5 ing a thin sheet ofnon-reacting metal between the base plate 0 and the base portion 4,contamination and destruction of the refractory are avoided, or at leastconsiderably reduced. Such sheets are indicated at |02 in Figs. l and 3.The sheets are, of course, suitably formed to fit the construction andconfiguration of the hearth, ,being suitably apertured for the gas inletsystem and split in the middle, as shown, for expension and contraction.f

The modification of the hearth shown in Fig. 5 is similar insubstantially all respects to that XshoWn in Fig. l, except that thebase portion il constructed with piers for supporting the container, thepiers having alloy caps |22 for 2o preventing reaction between' therefractory and ythe mild steel base of the container. l

I have Vfound that a chromium nickel alloy containing 25% chromium, 12%nickel, balance iron, will suitably reduce the chemical reaction 25'between the refractorytile and mild steel base plate l of the containerin a bell furnace opcrating in the neighborhood from-1600 to 1800 F.,and utilizing `a substantially pure and fairly .dry protectiveatmosphere of hydrogen which. is maintained at a slight positivepressure higher than the pressure in the heating zone'betwrcn the hoodand the bell so that the gas leaks slowly through the sand seals,although it may be withdrawn in greater amounts through outlet pipes |24when a large flow of the protective atmosphere is desired in theheat-treatment chamber 34.

While I have shown my inventionin forms which I now prefer, it isobvious that many 40 changes may be made in the details thereof andequivalents employed. I

I claim as my invention: 1.`A furnace for'heat-treating a charge in agaseous atmosphere, comprising a base portion, a container having abottom and sides, said container comprising a plurality of sectionssupported by said base portion, relatively movable covering means forcovering the spaces between said sections, a nely divided refractory bedin said container, a charge-supporting plate means on said bed, and gasconveying means comprising a plurality of pipe means embedded insaidbed, each of ,said pipe means being associated with a diierent one ofsaid sections. 2. In a furnace, the combination 'with acharge-supporting hearth means, of a raisable and 'lowerable hoodcooperating therewith for providing a heat-treatment chamber in whichcharges are heat-treated in a controlled .atmosphere; saidcharge-supporting hearth means comprising an elongated non-metallicrefractory base portion; a container supported by said base portion,said container containing a divided material; anges means. dependingfrom said container along its edges; a gas-sealing means comprisinggenerally U-shaped channel means around said base portion, said channelmeans having gas-sealing medium therein, the bottoms of said hood andsaid flanges being disposed in said gas-sealing medium; saidcontaineigilange means, and channel means being formed of spacedsections for permitting expansion and contraction, and limiting the-displacement thereof whereby any single displacement of said flangemeans in said channel means is less than said channel means spacedslightly from said` 3. In a furnace, the combination with acharge-supporting hearth means, of a raisable and lowerable hoodcooperating therewith for providing a heat-treatment chamber in whichcharges are heat-treated in a controlled atmosphere; saidcharge-supporting hearth means comprising an elongated non-metallicrefractory base portion, a heat-resistant metal on, and

in contact with, said refractory base portion, said metal being of atype substantially chemically inert with respect to said refractory baseportion in the presence of hydrogen at high temperatures; a containeron, and in direct contact with, said heat-resistant'metal, saidcontainer containing a divided material; iiange means depending fromsaid container along its edges; a gas-sealing means comprising generallyU-shaped channel means around said base portion, said channel meanshaving gas-sealing medium therein, the bottoms of said hood and saidflanges being disposed in said sealing medium; said container, flangemeans, and channei means being formed of spaced sections for permittingexpansion and contraction,l and limiting the displacement thereofwhereby any single displacement of said flange means in said channelmeans is less than the# total displacement; covering means for keepingthe spaces between saidsections covered at all times; conduit means fordirecting controlled atmosphere l from outside of said heat-treatmentchamber to the inside of said heat-treatment chamber, said conduit meanscomprising substantially horizontally arranged preheatingpipe meansdisposed in said divided material, and duct means connected to saidpreheating pipe means, said duct means opening below said container,said heat-resistant metal having an opening around said duct means, saidpreheating pipe means having gas outlets at said channel means near thelower edge of said hood and above sraid gas-sealing medium; and guidemeans for guiding said hood during lowering for positioning said hood insaid channel means slightly spaced from said "gas outlets.

4. In a furnace, the combination with a raisable and lowerable hood, ofa charge-supporting hearth means cooperating therewith for providing aheat-treatment chamber in which charges are heat-treated in a controlledatmosphere, said charge-supporting hearth means comprising an elongatednon-metallic refractory base portion, a container supported Iby said-loase Iportion. said container comprising spaced sections andrelatively movable covering means for covering the spaces between saidsections, said container containing a finely divided material andcomprising a base plate, conduit means for directing controlledatmosphere through said hearth means to said heat-treatment chamber,said conduit means comprising substantially horizontally arrangedpipemeans disposed in said finely divided material, said conduit meanshaving gas-outlet duct means extending through said base plate to saidpipe means, a gas-distributing chamber -below said base plate into whichsaid duct means opens, and gas inlet means for conveying controlled,atmosphere to said gas-distributing chamber.

5. In a furnace, the combination with a raisable 'and lowerable hood, ofa charge-supporting hearth means cooperating therewith for providing aheat-treatment chamber in which charges are heat-treated in a controlledatmosphere, 'said charge-supporting hearth means comprising an elongatednon-metallic refractory base portion, a container supported by said baseportion, said container containing a finely divided material andcomprising a base plate, conduit means for directing controlledatmosphere through said hearth means to said heat-treatment chamber,said conduit means comprising substantially horizontally arranged pipemeans disposed in said finely divided material, said conduit meanshaving gasoutlet duct means extending through said base plate to saidpipe means, a gas-distributing cham- -ber below-said base plate intowhich said duct' means opens, andfgas inlet means for conveyingcontrolled atmosphere to said gas-distributing chamber, said gas inletmeans comprising a gasV inlet pipe having a discharge end in saidgasdistributing chamber, andgas-sealing means for said discharge endpermitting said inlet pipe to expand and contract.

6. A heat-treating furnace for heat-treating a charge at relatively hightemperatures while the charge is enveloped yby a controlled reducing at-

